1. Field of the Invention
The present invention relates to a power supply unit for a fusing roller of an electrophotographic image forming apparatus, and, more particularly, to a power supply unit for a fusing roller of an electrophotographic image forming apparatus with improved durability and operating safety.
2. Description of the Related Art
In a general electrophotographic image forming apparatus adopting an electrostatic development technique, such as a photocopy machine or a laser printer, an electrostatic charging roller adjacent to a photoreceptor drum charges a photosensitive material coated on the surface of the photoreceptor drum while rotating around the photoreceptor drum. The charged photoreceptor material is exposed to a laser beam emitted from a laser scanning unit (LSU) so that a latent electrostatic image is formed in an intended pattern on the photosensitive material. A developer unit supplies toner to the photosensitive material to develop the latent electrostatic image formed thereon into a visible toner image. A predetermined transfer voltage is applied to the photoreceptor drum having the toner image and a transfer roller is put in contact with the photoreceptor drum by a predetermined force. In this state, as a print paper is fed in the gap between the transfer roller and the photoreceptor drum, the developed toner image on the photoreceptor drum is transferred to the print paper.
A fixing unit including a fusing roller instantaneously heats the print paper to which the toner image is transferred, to fuse and fix the toner image to the print paper. The surface of the fusing roller is heated to a predetermined temperature by radiant heat generated by a heat source of the fixing unit. The heat source of the fixing unit is connected with an external power source and generates radiant heat from an electric current supplied from the external power source.
A direct surface heating roller apparatus includes a heating roller that includes a roller body, an insulating layer coated on the roller body, a resistive heating layer coated around the insulating layer for generating heat, a protective layer formed on the resistive heating layer, and a power supply unit. The power supply unit is formed as a slip ring to fit around the heat-generating layer and is fixed in position with a conductive adhesive. The slip ring transfers electric current applied from the external power source to the heat-generating layer while rotating along with the roller body.
For the power supply unit of the direct surface heating roller apparatus described above, the resistive heating layer is formed in contact with the surface of the roller body and the slip ring fits around the resistive heating layer by spreading the conductive adhesive on the resistive heating layer. Thus, there can be a problem in that the power supply unit is subjected to electrical and mechanical stresses caused by electric current and residual heat, and thermal impacts that can occur depending on user circumstances. Because there is a need to raise the temperature of the heating roller apparatus to a high temperature within a short period of time, the power supply unit can experience repetitive thermal impacts in the initial operating stage and during normal operation. As a result, there can be a risk of electrical sparking and, thus, satisfactory durability and operating safety can be adversely affected. In addition, due to use of the conductive adhesive, it is likely that electric current will flow through components other than the resistive heating layer and, thus, a user possibly could get shocked.
Therefore, there is a need to ensure increased safety in operating the fusing roller unit using a heat pipe with a power supply unit differing from that typically used for a direct surface heating roller apparatus.